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Set Modifiers In ETABS

Set Modifiers In ETABS

Set Modifiers In ETABS

(OP)
Dear All,
In ETABS while assigning the frame section we give certain values in SET Modifiers option. Especially for torsional constant, Moment of inertia abt 2 axis, Moment of inertia abt 3 axis.
On what basis do we give these values. For eg if am using a Column of size 200x600mm what will be the Set modifiers that I have to give? please help me guys...

RE: Set Modifiers In ETABS

I generally apply 0.7 to M2, M3 and T (M1). A 200x600 column probably would only attract a small torsional moment which would not be critical to the design.

RE: Set Modifiers In ETABS

(OP)
thank you asixth.... But can you tell me why do u take that value or how did u get at that value... Its for my knowledge

RE: Set Modifiers In ETABS

Codes normally suggest 0.7 modifier for compression elements and 0.35 for flexural elements. I have not found too many suggestions for torsional multipliers except in the Australian bridge code which suggests as low as 0.1. Depends on how everything is meshed. I only use ETAB's for lateral analysis in which I keep the mesh for the floor slab very coarse (2-3 meters) using shell elements so there is never much torsion which get's put into the column.

I have found that unless it is an equilibrium torsion than the column element will not be too sensitive to variations in the torsion modifier.

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